Semi-continuous process centrifuges may operate by feeding a fluid comprising a liquid-solid suspension into a rotating bowl, sedimenting solids, and discharging liquid until the bowl is filled or is substantially filled to capacity with solids. Once the bowl is filled to capacity with solids, bowl rotation is stopped and the solids are discharged from the bowl. Thereafter, the next cycle in the process is initiated by again feeding the fluid into the rotating bowl, sedimenting solids, discharging liquid, followed by discharging the solids when the bowl is once again sufficiently filled.
Some types of semi-continuous centrifuges operate at relatively lower rotational speeds while the bowl is being filled with fluid from an empty state to avoid excessive vibrations (caused by the fluid sloshing around in the unfilled space of the bowl). In some centrifuges (e.g., a ViaFuge manufactured by Pneumatic Scale Angelus), a user visually monitors the centrifuge to determine when the bowl is filled with fluid, at which point the user stops the feed pump and manually increases the rotational speed of the filled bowl to correspond to the appropriate processing speed for the liquid-solid suspension that is to be separated. Upon reaching the appropriate increased rotational processing speed, the pumping of the fluid into the bowl is resumed. When the desired amount of fluid has been processed, and/or the bowl is filled with a maximum level of solids, the bowl rotation is stopped and the solids collected in the bowl are discharged.
In this system, a user visually determines when the bowl is filled with the fluid by observing when liquid begins to overflow from a discharge port. The composition of the overflowing liquid may be either feed suspension or liquid separated from the suspension, which is called centrate. In other types of centrifuges (e.g., a UniFuge manufactured by Pneumatic Scale Angelus), the centrifuge may employ automatic controls which optically sense the fill level in the bowl, in order to automatically control when to stop the feed pump and increase the rotational speed of the bowl.
Unfortunately for each of these examples, various circumstances may degrade the ability of these systems to consistently determine when a bowl is filled with the fluid, which can negatively affect the processing rate of the systems and/or cause carry-over of feed solids into centrate. For example, manually operated systems are susceptible to human error as to when liquid begins overflowing through the centrate discharge port. Also, automatic systems may be susceptible to the accumulation of small amounts of residual solids or foam in a sensing zone at which the presence of liquid is being detected optically. This effect can interfere with optical sensing of the actual fill level of the bowl. Further, the monitoring of liquid that has overflowed from the bowl into a discharge port (e.g., with a manual system or an automated system) can result in some contamination of the liquid exiting the discharge port with feed solids during each bowl filling cycle. Thus there is a need for improvement to existing centrifuge designs.